Improve the speed of adding tokens from added_tokens.json (#10780)

* use bisect to add one token to unique_no_split_tokens

* fix style

src/transformers/tokenization_utils.py

@@ -16,6 +16,7 @@
  Tokenization classes for python tokenizers. For fast tokenizers (provided by HuggingFace's tokenizers library) see
  tokenization_utils_fast.py
 """
+import bisect
 import itertools
 import re
 import unicodedata
@@ -99,6 +100,19 @@ def _is_start_of_word(text):
     return bool(_is_control(first_char) | _is_punctuation(first_char) | _is_whitespace(first_char))
 
 
+def _insert_one_token_to_ordered_list(token_list: List[str], new_token: str):
+    """
+    Inserts one token to an ordered list if it does not already exist. Note: token_list must be sorted.
+    """
+    insertion_idx = bisect.bisect_left(token_list, new_token)
+    # Checks if new_token is already in the ordered token_list
+    if insertion_idx < len(token_list) and token_list[insertion_idx] == new_token:
+        # new_token is in token_list, don't add
+        return
+    else:
+        token_list.insert(insertion_idx, new_token)
+
+
 @add_end_docstrings(INIT_TOKENIZER_DOCSTRING)
 class PreTrainedTokenizer(PreTrainedTokenizerBase):
     """
@@ -199,9 +213,15 @@ class PreTrainedTokenizer(PreTrainedTokenizerBase):
 
         # Make sure we don't split on any special tokens (even they were already in the vocab before e.g. for Albert)
         if special_tokens:
+            if len(new_tokens) == 1:
+                _insert_one_token_to_ordered_list(self.unique_no_split_tokens, new_tokens[0])
+            else:
                 self.unique_no_split_tokens = sorted(set(self.unique_no_split_tokens).union(set(new_tokens)))
         else:
             # Or on the newly added tokens
+            if len(tokens_to_add) == 1:
+                _insert_one_token_to_ordered_list(self.unique_no_split_tokens, tokens_to_add[0])
+            else:
                 self.unique_no_split_tokens = sorted(set(self.unique_no_split_tokens).union(set(tokens_to_add)))
 
         return len(tokens_to_add)